Microsporidia are obligate intracellular opportunistic protists that have been known to infect animals for more than 150 years. However, it was in conjunction with the AIDS epidemic that microsporidia were determined to be an important pathogen in immunosuppressed humans. Interestingly, microsporidia are commonly found in the environment and are important pathogens of many economic and agricultural animals. When cultivated in vitro, microsporidia spores adhere to host cell surfaces. Our previous studies showed that this adherence is mediated by host cell surface sulfated glycosaminoglycans and can be inhibited with addition of exogenous sulfated glycans. We have also shown that adherence can be augmented with certain divalent cations. Most importantly, when spore adherence is inhibited or augmented, host cell infection clearly decreases or increases, respectively, indicating a direct link between spore adherence and host cell infection. This novel revelation represents a significant advancement for microsporidia research. In light of this discovery, we hypothesize that microsporidia adherence to host cells is a critical step in the initiation of spore activation leading to host cell infection. The overall goal of this proposal is to develop a mouse intestinal loop model to test and quantify our in vitro derived spore adherence and infection hypothesis in an in vivo setting. The Specific Aims that address the overall goal are: 1) establish a mouse intestinal loop model to study microsporidia spore adherence in vivo, and 2) determine the effectiveness of using the intestinal loop model to study host cell infection in vivo. Understanding the role of spore adherence in activation and infection in an animal model will be valuable in developing and testing novel therapeutics. PUBLIC HEALTH RELEVANCE Microsporidia are pathogens, most often found in contaminated water, which can cause severe diarrhea in persons with weakened immune systems. This proposal is geared toward developing an animal model to test our hypothesis of how the organism makes the initial contact with cells, which ultimately leads to infection and symptoms. By knowing how this process occurs, we may be able to develop more effective treatments. [unreadable] [unreadable] [unreadable] [unreadable]